The present disclosure relates generally to engine covers, such as valve or rocker covers, and more particularly to an apparatus and method for mounting the engine cover on an engine.
The use of overhead valve and overhead cam engines is well known in the automotive and motorcycle industry. These engines have several distinguishing features, one of which is a valve cover mounted on the cylinder head. The valve cover defines the upper portion of either the rocker box (for overhead valve engines) or the cam case (for overhead cam engines).
The valve cover is typically a cast, stamped, or molded one-piece rigid structure that has a lower peripheral edge corresponding in shape to the upper peripheral edge of the cylinder head. The valve cover is mounted on the cylinder head over the valve drive (e.g., rockers or cams and valves). A sealing gasket is commonly used to seal the joint between the cylinder head and the valve cover.
In general, conventional gaskets require a relatively high compressive load between the members being sealed in order for the gasket to provide an effective seal. For example, a gasket placed between two stationary members, such as an engine block and an oil pan, or an cylinder head and a valve cover, is compressed between these elements. However, while producing an effective seal, these highly compressed gaskets can become a medium for transmitting noise, vibration and harshness (NVH) characteristics between the two members. That is, the vibration load input from one member is easily transferred through either the gasket or direct contact with the other member. Moreover, in these applications that require the high compressive sealing load, the number and placement of fasteners must compensate for deflections of the cover caused by the high loading conditions in order to assure a good seal.
Examples of such conventional gaskets requiring a high sealing load between the members include an elastomeric gasket shaped as an O-ring or similar shape, as well as an edge bond gasket, a carrier gasket, and a rubber coated metal (RCM) gasket. Since all of these conventional gaskets require a high compressive sealing load to assure an effective seal between the members, the effectiveness of vibrational isolation of one member from the other is poor. Another example of a conventional gasket is one formed from a room temperature vulcanization (RTV) located between the two members. The RTV is applied as a liquid in a thin layer and cures when exposed to air. For effective sealing with the RTV, however, it requires a hard mount between the members, which also provides poor vibration isolation.
It is known in the art relating to engine valve and rocker covers to provide a gasket and grommet mounting in a noise isolation system which interrelates the sealing performance and noise isolation in a robust cover design. Noise isolation is provided by mounting a cover with a grommet at each hold down bolt location and by a peripheral molded seal or gasket between the cover and the engine cylinder head or block which separates the cover from direct metal to metal contact (see FIG. 3). However, there are always one or more issues with respect to at least one of the proper number of bolts, the span between bolts, overloaded grommets, under loaded gaskets and the structural integrity of the cover. More specifically, the forces required to seal the molded gasket may be unevenly applied because of variations in the bolt pattern and spacing resulting in differing grommet loads and sealing variations at various locations around each part. Control of noise isolation may be compromised due to non-uniform compression sealing of the gasket, varying grommet loads and reaction distortions in the cover.
Accordingly, a cover mounting system which maximizes NVH isolation, provides an adequate uniform sealing function and minimizes structural requirements is desired.